1. Field of the Invention
This invention relates to circuits for counting user defined events occurring within a digital electronic circuit or device, and for recording the time at which the count reaches a user defined threshold.
2. Prior Art
Electrical circuits for performing a count and compare function on a digital electrical circuit are known, as are digital circuits for generating timing signals. D. S. Foreman in U.S. Pat. No. 4,008,404 discloses a digital interval timer which counts seconds and compares the value to a user defined threshold value.
Logic analyzers are complex diagnostic circuits utilized to determine the state of various registers and operations within digital computers. They are relatively large devices designed specifically to monitor computers. Typically they compare bit patterns in a first register with bit patterns in a second register and generate a trigger signal when a match occurs. Some logic analyzers operate in a further mode wherein the timing of computer control signals is monitored. Logic analyzers are used to debug computers by noting timing "gliches" and erroneous bit patterns. Traczy-Hornach in U.S. Pat. No. 4,241,416 discloses a logic analyzer particularly adapted to monitor microprocessors.
A further form of logic analyzer is the composite logic analyzer. A composite logic analyzer displays timing and state data simultaneous. Shimizu in U.S. Pat. No. 4,364,036 discloses a composite logic analyzer wherein the timing relationship between the timing and state data is correlated on a signal display.
Heretofore, however, a device has not been disclosed which is easily integrable, functions at high speed, is capable of continuously monitoring digital electrical circuits by counting virtually any user defined event and can time the period between two such events.